My 1990 240DL suddenly developed idle control issues. It stumbles and stalls during cold starts, and has loss of power/driveability issues until warmed up.

I'm using Bentley to trouble-shoot and have done the following:
-Ran diagnostic control function #1: No fault codes detected (1-1-1 reading)
-Ran diagnostic control function #2. Steps 1-10 had nominal readings, but step 11 (holding brake and changing gears on the AT) was abnormal (the LED just kept flashing rapidly).

Based on those results it seems that I have an idle control issue according to the book (thanks Bentley! Like I didn't know that).

Besides running the diagnostic tests I have:
-Checked the throttle control switch (ok)
-Sprayed the injector seals to check for leaks. Fluid stays around base of injectors for a while before it (I assume) evaporates. So I think those are good
-Checked for vacuum hoses loose or cracked (haven't found any)
-Inspected the throttle control valve (there was a little oily gunk in the body but didn't really seem that bad.

On my list of things to check I now have:
-Air Control Valve
-EGR Valve
-Transfer fuel pump operational?
-Air Mass Meter
-Coolant temp sensor (or an I assume this is good since no engine codes??)
-Test fuel pressure (saving this one for last)
-Test oxygen sensor
-Look some more for broken wires/connectors
-Look for bad ground wires
-Check the ECU

I'd appreciate any advice on which are most likely to be the culprit and which order to tackle these in.

Thanks in advance!

I'd clean the throttle plate/body first and make sure its adjusted correctly. I think procedure is in 7/900 FAQ. I would also clean the idle air control valve as they get sticky from dirt/grime. This does it most of the time. Good luck. Mike

Wanted to close out this thread by reporting how the issue was resolved.

After suffering through the problem without being able to/having the time to sort it out myself I brought the car to a local independent shop that fiddled with it over the course of a month-plus without being able to figure the problem out. Finally gave up on them and drove it the 20 miles to the nearest dealer that I trust/have had good experience with in the past(Merrimack Street Volvo, Manchester NH).

They had the car for a day and diagnosed the problem as a bad fuel pressure regulator. They replaced the FPR, cleaned the throttle body as suggested here, and the problem is solved. Total cost was $238.05

In retrospect I wish I'd gone to the dealer to start off with.

Thanks much Mike; will post results after completing those items. Also appreciate the reference to the FAQ.